Fluid catalytic cracking

Abstract

A method for maintaining a desired catalyst regeneration temperature in a fluid catalytic cracking unit operating with complete combustion of coke to carbon dioxide when the coke content of the spent catalyst supplied to the regeneration zone from the reaction zone is insufficient to maintain the temperature in the regeneration zone necessary for complete combustion of coke to carbon dioxide in which residual liquid hydrocarbon from the cracking reaction zone is introduced into contact with partially spent cracking catalyst at cracking reaction temperature effecting conversion of said residue to volatile reaction products and additional coke deposit on the spent catalyst in an amount sufficient to maintain the temperature in the regeneration zone necessary for complete combustion of coke to carbon dioxide and substantially complete removal of carbon from the catalyst.

I claim: 
     
       1. In a continuous fluidized catalytic cracking process comprising cracking a naphtha or gas oil feedstock in a riser transport reaction zone and separating hydrocarbon vapor reaction products from coke-contaminated spent catalyst in a reaction-separation zone comprising a fluidized bed of spent catalyst, stripping said spent catalyst in a stripping zone, and regenerating stripped spent catalyst in a regeneration zone wherein coke-contaminated spent catalyst is regenerated at a temperature in the range of from about 1250° F. to about 1500° F. by contact with an oxygen-containing regeneration gas in an amount in excess of the amount theoretically required for complete combustion of coke on said spent catalyst to fully oxidized reaction products effecting substantially complete removal of coke from said catalyst and production of a flue gas comprising nitrogen and carbon dioxide substantially free from carbon monoxide and wherein the coke produced by cracking said feedstock is insufficient for providing heat required to maintain said temperature in said regeneration zone and a high carbon content residual hydrocarbon liquid product from said catalytic cracking process is introduced into said reaction-separation zone into intimate contact with said fluidized bed of coke-contaminated spent catalyst separated from said hydrocarbon vapors effecting cracking of said residual hydrocarbon to hydrocarbon vapors and an additional amount of coke deposit on said spent catalyst, the improvement which comprises supplying a sufficient additional quantity of oxygen-containing regeneration gas to said regeneration zone to consume said additional coke deposit and maintaining an excess of oxygen over that required for complete combustion of said coke including said additional amount of coke on said catalyst and from one to ten mole percent oxygen and from about 0 to about 500 parts per million by volume carbon monoxide in said flue gas, increasing the amounts of said residual hydrocarbon and additional regeneration air when the temperature in said regeneration zone decreases and decreasing the said amounts when the temperature in said regeneration zone increases. 
     
     
       2. A process as defined in claim 1 wherein said oxygen is supplied in an amount sufficient to maintain an oxygen concentration in the range of two to five mole percent in said flue gas. 
     
     
       3. A process as defined in claim 1 wherein said residual hydrocarbon fraction from said cracking reaction products is introduced into said reaction-separation zone as a dispersion of atomized liquid in steam. 
     
     
       4. A process as defined in claim 1 wherein said fluidized bed temperature in said reaction-separation zone is within the range of 700° to 1000° F. 
     
     
       5. A process as defined in claim 1 wherein the carbon on the regenerated catalyst is maintained within the range of from about 0.01 to about 0.10 weight percent. 
     
     
       6. A process as defined in claim 1 wherein said catalyst regeneration temperature is in the range of 1275° F. to 1450° F.